The present invention relates to a locating and locking unit for sheet metal parts which are for assembling on a motor-vehicle body by electric spot-welding.
Plants for assembling motor-vehicle bodies by electric spot-welding are already known, of the type comprising:
a movable positioning frame on one side of the assembly line, parallel to the line and movable between a working position in a welding station and waiting position spaced apart therefrom,
wherein the said positioning frame includes a self-propelled lower trolley running on rails positioned parallel to the assembly line and an upper part free of guides, carrying locating and locking devices for locking the parts to be welded in the correct assembling position, and
a base platform, situated at the side of the line at the welding station, for receiving the positioning frame when this is brought to its working position, the said platform being able to move transversally with respect to the line to bring the positioning frame received thereon to a position closer to the axis of the line for engaging the parts to be welded.
Assembling plants of the above-described type are disclosed in, for example, EP-A-0 642 878 and EP-A-0 835 717, in the name of the same Applicant.
The object of the present invention is to provide a locating and locking unit having the above described features which is simple, reliable and with reduced dimensions, and which is particularly suitable for assembling individual elements or small subgroups on a motor-vehicle body which is being assembled.
To achieve this object, the invention provides a locating and locking unit having the above indicated features and also characterized in that the aforesaid base platform is pivotably mounted on a fixed support structure around an axis parallel to the line.
The base platform can be moved between a substantially horizontal first position, suitable for receiving the trolley of the positioning frame, and a second position, rotated towards the assembly line for engagement of the positioning frame on the parts to be welded, said unit also including motorized means for driving the movement of the base platform, including a crank rotatable on the fixed support structure and carrying a pin that is slidably engaged in a slot made in a bracket of the base platform.
According to an additional feature, the base platform is equipped with a locating element that has a cavity with a V-shaped surface suitable for engaging itself in the aforesaid rotated position of the base platform over the surface of a cylindrical element freely rotatably mounted on the fixed support structure around an axis that is parallel to and slightly offset from the articulation axis of the base platform, for providing a reference for the precise position of the base platform along two orthogonal axes in a plane that is perpendicular to the line.
A further feature of the invention lies in that the said base platform is equipped with a pair of freely rotatable rollers, whose axes are vertical when the platform is in its horizontal position, and suitable for engaging with the two sides of a wedge-shaped element carried by the fixed support structure when the platform is brought into the aforesaid rotated position, for providing a reference for the precise position of the base platform along an axis parallel to the line.
In addition, the aforesaid base platform and/or the aforesaid positioning frame are equipped with engagement elements suitable for cooperating, in the aforesaid rotated position of the base platform, with locking clamps carried by the fixed support structure to stably lock the positioning frame.